Multiple middle-of-line (MOL) levels have been designed at the 7NM node to provide wiring flexibility for system on chips (SOC) applications. Contact levels, such as TS, CA/CB and MO levels, make up the MOL contact levels that need to be metallized.
As interconnect contact dimensions shrink, other gap fill materials are being considered as replacements for tungsten (W) based contacts. Titanium (Ti) based liners are necessary to form source/drain silicide contact at TS level and act for gettering oxygen at the CA/CB/MO levels. A thin atomic layer deposition (ALD) titanium nitride (TiN) barrier is also required to improve adhesion of alternative gap fill materials. However, RF physical vapor deposition (PVD) Ti liner deposition causes overhang at the top of the trench feature, often referred to as bread loafing, leading to a re-entrant profile, which is challenging for gap fill and leads to voids being formed during metal fill processes.